Balancing Running Times Between Master And Slave; Staring The Follower Unit; Abnormal Operating Conditions; Controlling A Pro-Dialog Unit With A System Manager - Carrier 30GX Installation, Operation And Maintenance Instructions

All control commands to the master/slave assembly (start/stop,
setpoint, load shedding, etc.) are handled by the unit which is
configured as the master, and must therefore only be applied to
the master unit. They will be transmitted automatically to the
slave unit. Therefore to start up the assembly, simply validate
operating mode CCN (i.e. CCn) on the master unit (with the
CCN start/stop variable previously forced to Enable). The slave
unit stays in CCN operating type continuously. To stop the
master/slave assembly, select Local Off (LOFF) on the master
unit. In some cases with a specific configuration, remote volt-
free contacts can be used to control unit start/stop or to select
setpoint 1 or 2, even though both units are still in CCN
operating mode.
NOTE: All parameters required for the master/slave function
must be configured by Carrier Service.

5.18.2 - Balancing running times between master and slave

The master unit (depending on its configuration) may have as
part of its functions to designate whether the master or slave is
to be the head machine or the follower. The roles of head
machine and follower will be reversed when the difference in
running hours between the two units exceeds a configurable
value, ensuring that the running times of the two chillers are
automatically equalised. The changeover between head
machine and follower may take place when the assembly is
started up, or even whilst running.
The running time balancing function is not active when:
• It has not been configured: in this case the head machine is
always the master unit.
• A demand limit is applied to the master unit: in this case the
head machine will always be the master unit until the
demand limit is lifted.
5.18.3 - Starting the follower unit
The head machine will always be started first. When the head
machine is at its full available capacity, the start-up delay
(configurable) is initialised on the follower. When this delay
has expired, and if the error on the control point is greater than
1.7°C, the follower unit is authorised to start and the pump is
activated. The follower will automatically use the master unit's
active setpoint. The head machine will be held at its full
available capacity for so long as the active capacity on the
follower is not zero. When the follower unit is commanded to
stop, its cooler water pump is turned off with one minute delay.

5.18.4 - Abnormal operating conditions

In the event of a communication fault between the two units,
each shall return to an autonomous operating mode until the
fault is cleared. If the master unit is halted due to an alarm, the
slave unit shall be authorised to start without prior conditions.
5.19 - Controlling a Pro-Dialog Plus unit with a
System Manager
Up to 8 PRO-DIALOG Plus units (or System Manager
compatibles) can be controlled by one control module of the
FSM or CSM III type which can handle multi-tasking of control
functions such as starting units in sequence.

5.20 - Optional heat reclaim module

This option only applies to air-cooled units, equipped with a
water-cooled heat reclaim condenser. An additional 4 x DO
board must be installed. This board permits control of:
- two solenoid shutoff valves for the heat reclaim coil, one
per circuit.
- two drain solenoid valves, one per circuit. These permit
draining the refrigerant from the inactive coil, when the
unit changes over from the cooling mode to the heat
reclaim mode.
Selecting the heat reclaim mode can be done with either the
local interface or remotely with the (recl_sw) contact or by
CCN.
The heat reclaim function is active when: the heat reclaim
entering water temperature is lower than the heat reclaim
setpoint, minus half of the heat reclaim dead band.
The heat reclaim function is not active when: the heat reclaim
entering water temperature is higher than the heat reclaim
setpoint, plus half of the heat reclaim dead band.
In the dead band the function remains in its active mode. The
default value of the dead band is 4.4°C. This value can be
modified by Carrier Service.
Change-over procedure from cooling mode to heat reclaim
mode:
- Start-up of the condenser pump
- Verification of the condenser flow switch control contact.
If this remains open after one minute of condenser pump
operation, the circuit remains in cooling mode and alarm
83 for circuit A (alarm 84 for circuit B) will be activated.
- As soon as the saturated condensing temperature reaches
30°C and the superheat reaches 8.3 K, the pumpdown
sequence is activated.
- Pumpdown: closing of the cooling mode coil shutoff
valve. Opening of the drain valve, closing of the EXV
valve.
- As soon as the drain pressostat contact (contact pd_a_sw
for circuit A, item 10 of the INPUTS menu (contact
pd_b_sw for circuit B, item 11 of the INPUTS menu) is
open, the drain valve will close and the heat reclaim
function is active.
Item 17, hr_status, of the INFORMATION menu permits
consulting different heat reclaim function sequences:
hr_status with format n1n2 with:
n1 = sequence of circuit A
n2 = sequence of circuit B
0 = cooling mode
1 = heat reclaim mode selection
2 = pumpdown sequence
3 = effective heat reclaim mode
4 = pumpdown fault*
5 = water flow switch fault*
* Alarm 83 for circuit A or 84 for circuit B is activated. Consulting the
item hr_status gives cause as (4) or (5). Resetting of the alarms re-
initialises the information of hr_status.
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